Any writer will tell you that an appearance on Oprah is the fast-track to high book sales. For James Frey and his memoir, A Million Little Pieces, it was the ticket to bestseller status. The book,published in 2003, charts Frey's journey from drug-and alcohol-addicted criminality into clean literary giant. Frey's publisher described him thus: "In writing his beautiful memoir, James Frey does away with a lot of things: punctuation, standard grammar rules, 12-step programmes, belief in a higher power and, eventually, his addiction to alcohol and drugs."

Except, as revealed by the investigative website the Smoking Gun, it didn't quite happen like that. They found that much of Frey's nihilistic past, as recounted in the book, was simply not true. Frey had repeatedly asserted that his work was honest and non-fictional, yet the website unearthed evidence that most of the pivotal events in the book did not happen as described, if at all. Frey denied the allegations. Now though, he has been forced to acknowledge that the Smoking Gun's version of events is accurate.

Frey has since tried to perform a kind of literary sleight of hand by having a go at redefining memoir. In an interview with Larry King shortly after the story broke, Frey said: "I think of the book as working in sort of a tradition of what American writers have done in the past, people like Hemingway and Fitzgerald and Kerouac ... at the time of their books being published, the genre of memoir didn't exist ... Some people think it's creative non-fiction. It's generally recognised that the writer of a memoir is retelling a subjective story. That it's one person's event. I still stand by the essential truths of the book."

Is what he says about this "new genre" true? While most readers would recognise that a memoir is only the author's side of the story, it is assumed that the facts are as close as subjectively possible to what actually happened. We don't expect key events, upon which much of the book's "message" is hinged, will be fabricated. The genre whereby a writer intertwines the facts of his own story, with a fictitious plot isn't new, and already has a perfectly good name - the semi-autobiographical novel.

Does it really matter whether a memoir is embellished? Frey's "recovery" from drug and alcohol addiction is, according to him, "the primary focus of the book". I have been in recovery for over a decade, so I know that it's life-and-death stuff. One of Frey's key themes is that he "recovered" by force of will alone. No AA, no 12 steps, no support group; just him and his demons. The message is that if he can drag himself out of the pit of hell, then anyone can. Except he didn't.

Just think how dangerous that is. Addicts and alcoholics are desperate vulnerable people; if you're going to offer them a way out, you'd better be certain it works. But how can you be, if you haven't walked the path? The reader reviews for Frey's book on Amazon contain this nugget: "I've been to four funerals in the last 12 months. One of them was a guy who dropped out of AA/NA after reading Frey's crap - before it had been exposed as a fraud. He decided to follow Frey's advice ... He lasted about three months before he got high again. He was dead two months after that."

Frey claims his memoir has "emotional truth". But "emotional truth" is meaningless when it's woven around events that bear no relation to reality - unless you're writing fiction. This memoir was touted around publishers as a novel for a long time, unable to get a publishing deal. That should tell us everything.The book only works because we believe he really lived it. As fiction, it simply wasn't good enough.

· Niki Shisler's memoir, Fragile, will be published by Ebury Press in March